1. Technical Field
The present disclosure relates to a wireless network system, more particularly, to a wireless network system to which a plurality of devices operating on the basis of incompatible and different standards are connected and the plurality of devices operating on the basis of the respective standards can operate stably while being mixed.
2. Related Art
Process control systems in recent industrial automation are frequently configured using wireless field devices serving as a kind of wireless communication apparatus. As these wireless field devices, devices designed on the basis of the industrial automation wireless communication standard ISA100.11a drawn up by the ISA100 Committee of the International Society of Automation (ISA) and issued on September, 2009 are used, for example.
As a result that a related-art process control system is configured using wired field devices connected via cables, the process control system is affected by, for example:
1) Restriction on communication distance
2) Restriction on cable routing
Hence, sensors for measuring predetermined physical quantities serving as targets to be measured, such as temperature and flow rate, cannot be installed at optimal positions inside a plant, thereby causing a problem that the control accuracy of the process control system is degraded. The above-mentioned approach is taken to solve this problem.
FIG. 4 is a configuration explanatory view showing an example of a wireless network system having been used in the related art. In FIG. 4, a wireless network 1 is configured as a star-mesh topology composed of a plurality of I/O devices 2 to 6, routing devices 7 and 8, and a gateway 9.
The I/O devices 2 to 6 have the wireless communication functions specified in the ISA100.11a and include various sensors, such as differential pressure/pressure transmitters and temperature transmitters, and various final control elements, such as valves and positioners.
The routing devices 7 and 8, serving as advertisement routers, have functions for periodically issuing advertisement to neighboring devices, thereby transmitting route information and messages. These routing functions may be provided for sensors, such as differential pressure/pressure transmitters and temperature transmitters, and final control elements, such as valves and positioners, in some cases.
The gateway 9 has a function for connecting the wireless network 1 to a plant network 10 and also has a function for connecting the plurality of I/O devices 2 to 6 to a host application 11 provided for the plant network 10.
Furthermore, the gateway 9 can be equipped with a system manager function and a security manager function for the wireless network topology as necessary, thereby being capable of managing the system and security of the wireless network topology. Moreover, the gateway 9 can be equipped with a backbone router function for performing connection to wireless connection devices.
The host application 11 performs the setting of the routing devices 7 and 8 and the I/O devices 2 to 6, the diagnosis of devices, and the upgrade of firmware.
When attention is paid to wireless communication inside the wireless network 1 configured as shown in FIG. 4, the I/O devices 2 and 3 perform communication with the gateway 9 via the routing device 8, and the I/O devices 4 to 6 perform communication with the gateway 9 via the routing device 7.
When the above-mentioned wireless communication is performed, in order that the presence or absence of transmission errors is identified accurately, the calculation result of an MIC (Message Integrity Code: manipulation detection code) based on a cipher set beforehand on the transmitting side is added and transmitted. Also on the receiving side, an MIC is calculated on the basis of a cipher key common to the transmitting side, and the result of the calculation is compared and checked with the received MIC. The presence or absence of transmission errors is then judged depending on whether the two MICs are coincident with each other.
FIG. 5 is a block diagram showing an example of a processor 20 on the receiving side, and FIG. 6 is a flowchart illustrating an example of the flow of MIC processing at the time when data is received in the processor 20 on the receiving side shown in FIG. 5. Referring to FIGS. 5 and 6, when a data receiver 21 receives data transmitted from the transmitting side (at step S1), an MIC detector 22 detects the MIC that was calculated and added to the data on the transmitting side (at step S2), and an MIC calculator 23 calculates an MIC on the basis of the cipher key common to the transmitting side (at step S3).
An MIC comparator 24 compares and checks the MIC detected by the MIC detector 22 with the MIC calculated by the MIC calculator 23, thereby judging whether the two are coincident with each other (at step S4).
In the case that the two are coincident with each other, the MIC calculated by the MIC calculator 23 is added to an acknowledge signal ACK generated by an ACK generator 25 and then transmitted to the transmitting side via a data transmitter 26 (at step S5).
On the other hand, in the case that the two are not coincident with each other, the MIC calculated by the MIC calculator 23 is added to a non-acknowledge signal NACK generated by an NACK generator 27 and then transmitted to the transmitting side via the data transmitter 26 (at step S6).
Non-patent Document 1 discloses a concept of a field wireless solution conforming to ISA100.11a and a concept of a field wireless system in which a central focus is placed on DCS.
Non-patent Document 2 discloses a technology relating to wireless field devices and a field wireless system conforming to ISA100.11a.
Patent Document 1 discloses a technology for preventing terminals from malfunctioning even in the case that a communication network is structured so that old terminals operating according to an old protocol existing already are mixed with new terminals adopting a new protocol that is made by modifying the old protocol.